1. Field of the Invention
The invention relates to a method for producing organopolysiloxanes.
2. Description of the Related Art
WO 2007/023084 A2 and EP 2072 591 A1 describe organopolysiloxane compounds comprising per molecule at least one structural unit of the general formula O3-a/2RaSi—Y—(SiRaO3-a/2)b, such as the structural unit O2/2MeSi—CH2CH2—SiMeO2/2. The described method for producing these compounds is the cohydrolysis of compounds of general formulae X3-aRaSi—Y—(SiRaX3-a)b and R1cSiX4-c, such as the cohydrolysis of 1,2-bis(methyldichlorosilyl)ethane with vinyldimethylchlorosilane.
This method has substantial disadvantages both when carried out as a continuous operation and when carried out batchwise. Cohydrolysis with compounds of formula R1cSiX4-c forms considerable quantities of undesired by-products exclusively comprising the structural moiety R1cSiO4-c and not the desired structural moiety O3-a/2RaSi—Y—(SiRaO3-a/2)b. The method moreover forms low molecular weight compounds which, while also comprising the desired structural moiety O3-a/2RaSi—Y—(SiRaO3-a/2)b, need to be removed on account of their undesired properties (e.g. low boiling point), as is described in Example 1 of WO 2007/023084 A2. This leads to a more costly and inconvenient removal step and also to reduced yield of the target product and thus a low space-time yield.
As is apparent from DE 2630744 A1, organosiloxanes may be converted by reaction with chlorosilanes in the presence of activated carbon. Disadvantages of this method include the high temperatures, close to the boiling range of the components, and the large quantities of inorganic acids added, as is apparent from the examples.